Comment Re:Load shifting (Score 2) 156
I'm not a router expert, but...
Routing uses the process of receiving a packet and checking its destination. Using a table lookup based on the destination, it finds the the neighboring router it should forward the packet to. The table is updated so that routing can find 'the shortest path.' The real question here is how 'shortest' or distance is defined.
Your method of configuring geographic location on routers is basically trying to get the router to calculate its distance to its neighbors. However, you're thinking about geographic distance rather than logical topology which is the 'road map' that routers can travel on. There are two direct problems that stem from your method:
1. Pipe size (bandwidth) is not accounted for. If there exists two paths to the destination, should I take the 'geographically' shorter path that is connected by a 56K line, or a slightly longer path that consists of several OC3's?
2. Hop count is not weighed. With two paths, the geographically shorter path may travel through 20 routers, where a longer path may hop through 5 routers--how do you determine the tradeoffs?
Most importantly, routers currently have a mechanism to address this routing issue by allowing users to define the distance between routers. I believe this is usually set to reflect bandwidth size (ie. usually people define their OC3's to be shorter than their T1's). This is generally easier for network managers to adjust their link distances than to tweak their lat/lon coordinates.
Most of the problems with congestion I've seen is due to capacity problems--where there may be two different paths to a destination, but one path is over-utilized and another is under-utilized. Currently, routers are very limited in their load-balancing techniques. I believe Cisco routers can balance up to 6 equal paths--but configuring multiple 'equal' paths is not easy for a meshed network (equal as in defined distance). Without equal paths, routers generally send their packets down the 'shortest' path, regardless of congestion. Routers are not intelligent enough to recognize congestion and calculate the 'next shortest path' (though 'next-shortest' paths are done when there is a link failure). Without this type of mechanism, if you were to get the router to use the 'path of least resistence,' it would just shift the congestion from the previous route to your newly defined route. Currently, the MPLS initiative is trying to address this capacity issue.
Routing uses the process of receiving a packet and checking its destination. Using a table lookup based on the destination, it finds the the neighboring router it should forward the packet to. The table is updated so that routing can find 'the shortest path.' The real question here is how 'shortest' or distance is defined.
Your method of configuring geographic location on routers is basically trying to get the router to calculate its distance to its neighbors. However, you're thinking about geographic distance rather than logical topology which is the 'road map' that routers can travel on. There are two direct problems that stem from your method:
1. Pipe size (bandwidth) is not accounted for. If there exists two paths to the destination, should I take the 'geographically' shorter path that is connected by a 56K line, or a slightly longer path that consists of several OC3's?
2. Hop count is not weighed. With two paths, the geographically shorter path may travel through 20 routers, where a longer path may hop through 5 routers--how do you determine the tradeoffs?
Most importantly, routers currently have a mechanism to address this routing issue by allowing users to define the distance between routers. I believe this is usually set to reflect bandwidth size (ie. usually people define their OC3's to be shorter than their T1's). This is generally easier for network managers to adjust their link distances than to tweak their lat/lon coordinates.
Most of the problems with congestion I've seen is due to capacity problems--where there may be two different paths to a destination, but one path is over-utilized and another is under-utilized. Currently, routers are very limited in their load-balancing techniques. I believe Cisco routers can balance up to 6 equal paths--but configuring multiple 'equal' paths is not easy for a meshed network (equal as in defined distance). Without equal paths, routers generally send their packets down the 'shortest' path, regardless of congestion. Routers are not intelligent enough to recognize congestion and calculate the 'next shortest path' (though 'next-shortest' paths are done when there is a link failure). Without this type of mechanism, if you were to get the router to use the 'path of least resistence,' it would just shift the congestion from the previous route to your newly defined route. Currently, the MPLS initiative is trying to address this capacity issue.
